1. Field of the Invention
The present invention relates to an image recording apparatus which records an image by scanning a recording sheet with a light beam.
2. Related Background Art
FIG. 24 shows a conventional image recording apparatus disclosed in U.S. Pat. No. 4,665,408 which optically records an image on a recording sheet. As shown in the figure, non-used sheets 132 for recording are piled in a supply magazine 131. A suction device 134 connected to an air cylinder 133 is mounted above the leading edges of the sheets 132. The air cylinder 133 and the suction device 134 are vertically and pivotally movable on a shaft 135. When the air cylinder 133 and the suction device 134 move downward, the sheets 132 are upwardly by an air suction operation of the air cylinder 133 and the leading edge of the uppermost sheet among the piled sheets 132 is lifted up. A pair of feeding rollers 136, which are horizontally movable, begin to be rotatably driven in response to a start signal, then simultaneously move to the right in the figure, nip the leading edge of the lifted sheet, transport the sheet 132 onto a holding plate 137 by the rotation of the feeding rollers 136, and then the rotation operation is stopped.
A push lever 138 and a sheet correcting portion 140 are respectively pivotally movable on shafts 139 and 141 and retractable out of a sheet transport path. While the pair of feeding rollers 136 are transporting the sheet 132 from the supply magazine 131 to the holding plate 137, the push lever 138 is being retracted upward out of the transport path and the sheet correcting portion 140 enters the transport path.
When the sheet 132 is sent onto the holding plate 137 by the pair of feeding rollers 136, the push lever 138 rotates clockwise and pushes the end edge of the sheet 132 forward. At this time, the leading edge of the sheet 132 abuts against the sheet correcting portion 140 and the center portion of the sheet 132 is curved by the urging force of the push lever 138.
Subsequently, the push lever 138 rotates counterclockwise and releases the end edge of the sheet 132 from being urged. As a result, the sheet 132 is laid flat on the holding plate 137 and the position of the leading edge of the sheet 132 is precisely corrected so it will not be slanted by means of the sheet correcting portion 140.
Next, while the sheet correcting portion 140 rotates counterclockwise and retracts out of the transport path, the push lever 138 rotates clockwise and pushes the end edge of the sheet 132. As a result, the sheet 132 slides onto the holding plate 137 and the leading edge of the sheet 132 comes into a nip between a rotating subscanning drum 142 and nip rollers 143. The subscanning drum 142 is continuously driven to rotate counterclockwise during the recording operation and the nip rollers 143 are also rotated by the usual contact with the drum 142. The sheet 132 is transported to the left in the figure by the rotational force of the subscanning drum 142 the moment it is nipped between the drum 142 and the front nip roller 143.
An optical system unit 144 is mounted above the holding plate 137. A laser beam emitted from a laser source 145 is directed between the two nip rollers 143 through a mirror 146 and mainly scans the photoconductive recording sheet 132 which is being transported on the subscanning drum 142 so as to form a predetermined image.
The sheet 132, on which the image is thus formed, is fed from between the subscanning drum 142 and the rear nip roller 143 to the left in the figure, gradually hangs down from the leading edge thereof due to its own weight, and is stored in a receive magazine 147.
Next, referring to FIG. 25, another example of the prior art will be described. FIG. 25, like FIG. 24, shows a conventional image recording apparatus which optically records an image on a recording sheet and is disclosed in U.S. Pat. No. 4,754,292. Non-used recording sheets are denoted by 202a and piled and stocked in a supply magazine 202 which is almost horizontally mounted. A suction device 203 supported by a mechanism, not shown, is positioned near the right edge of the sheet 202a in the figure. The suction device 203, which can be retracted out of the supply magazine 202 by the support mechanism, comes into the supply magazine 202, sucks the uppermost sheet among the piled sheets, and then moves to the upper right in the figure and puts the sucked sheet into a pair of feeding rollers 204. The pair of feeding rollers 204 are rotatably driven by a driving mechanism, not shown, and transport the sheet 202a into a transport path constituted by guide plates 205 and 206. A pair of feeding rollers similar to 204 are denoted by 224 and further transport the sheet 202a, which is fed between the guide plates 205 and 206 to a transport path constituted by guide plates 207 and 208. When the end edge of the sheet 202a separates from the pair of feeding rollers 224, the sheet 202a falls due to its own weight, is guided by the guide plates 207 and 208, and then reaches a pair of feeding rollers 209. After that, the pair of rollers 209 rotate in a direction which ejects the sheet upward, correct the position of the sheet, and then reversely rotate so as to lead the sheet to a transport path constituted by guide plates 211 and 210 and make the leading edge of the sheet reach pairs of subscanning rollers 212 and 213. Reference numeral 221 denotes an optical system unit which is almost horizontally mounted below the supply magazine 202. A laser beam 221a emitted from a laser source, not shown, in the optical system unit 221 is irradiated onto the sheet nipped between the pairs of subscanning rollers 212 and 213 and forms a predetermined image on the sheet by scanning in a direction almost perpendicular to the transport direction of the sheet. After the recording is completed, the sheet is transported through a transport path constituted by guide plates 214, 216, 217, 219 and 220 by pairs of feeding rollers 215 and 218 and led to an automatic developing device 222.
However, the prior art shown in the above FIGS. 24 and 25 have the defects described below.
First, in the apparatus shown in FIG. 24, there is a problem that the apparatus is large owing to the construction thereof. The overall length of the holding plate 137 is a little longer than that of the sheet 132. Therefore, if the overall length of the sheet is L.sub.f, the distance L.sub.o between the recording device and the end edge of the piled non-used sheets is theoretically longer than 2L.sub.f and normally almost equals 3L.sub.f. In the case that a half-size (43 cm.times.35 cm) sheet is used and L equals 43 cm, the width of the apparatus must be approximately 130 cm and thus the apparatus is quite large.
In order to further shorten L.sub.o in the same prior art construction, it is necessary to shorten the overall length of the holding plate 137. In this case, it is quite likely that the trailing edge of the sheet 132 will remain in the supply magazine 131 when the recording is started, and will be in contact with the upper plane of the piled non-recorded sheets. As a result, it seems that the resistance force, which acts in the reverse direction to the above-mentioned transport direction of the sheet, becomes much higher than that of the prior art and furthermore changes rapidly. This is because the friction coefficient of the surface of the non-used recording sheet is higher than that of the holding plate 137 whose surface is smoothly treated. As a result, the surface of the non-used recording sheet is more disadvantageous than the surface of the holding plate 137 as the former surface is subject to static electricity and stickiness. Therefore, the transport speed of the sheet, that is, the subscanning speed becomes uneven and this causes deterioration of the image. Accordingly, in the apparatus of the prior art, it is difficult for L.sub. o to be shorter than 2L.sub.f.
On the other hand, in the prior art shown in FIG. 25, since the transport path is located in the lower portion of the apparatus in relation to the overall construction, a jamming recovery operation, or maintenance operations for a drive source, a drive mechanism, guide plates and so on must be performed from the side of the apparatus and such operations are difficult to carry out.
In addition, in the apparatus shown in FIG. 25, the sheet, which is being recorded, does not naturally hang down due to its own weight, but is against the own weight and the elasticity of the sheet. In other words, both the weight of the sheet and the elastic force of the curved sheet are added to the transport path. Therefore, the resistance force against transport in the subscanning direction and the change in resistance are large and a high-precision subscanning is difficult.